Field of the Invention
The present invention relates to an exhaust purifying apparatus that treats particulate matter in a passage in which a gas containing the particulate matter flows.
Description of the Related Art
Japanese Patent Laid-Open No. 2009-112916 discloses an example of an exhaust purifying apparatus for treating particulate matter (PM) contained in factory gases or in exhaust in automobiles, machines (including internal combustion engines) and the like. The exhaust purifying apparatus disclosed in Japanese Patent Laid-Open No. 2009-112916 includes an outer shell shaped in a tubular form, a dust trapping filter device composed of a dust trapping electrode arranged along an inner side of the outer shell and a dust trapping filter layer, and a discharge electrode disposed inside of the dust trapping filter device and arranged in the central part of a flow passage for exhaust containing the particulate matter. The discharge electrode includes a primary portion extending along the center axis of the outer shell and a plurality of projecting portions each projecting in a direction perpendicular to the center axis of the outer shell from the primary portion. The dust trapping electrode is conductive and is earthed through the outer shell. According to the description of Japanese Patent Laid-Open No. 2009-112916, a high voltage is applied to the discharge electrode to generate corona discharge on the circumference of the projecting portion of the discharge electrode, and the particulate matter in the exhaust takes charge with the corona discharge. The charged particulate matter can flow toward the dust trapping electrode as an opposing electrode by coulomb forces. As a result, an ion wind is formed in a direction perpendicular to the flow direction of the exhaust and the particulate matter is trapped in the dust trapping filter device. It should be noted that in an embodiment of Japanese Patent Laid-Open No. 2009-112916, the dust trapping filter device is formed in a bellows shape, thereby increasing a surface area of the dust trapping electrode to enhance a trapping rate of the particulate matter.